Mitigation Details 101

• Some Key Elements To Radon Mitigation
• Crawl Spaces
• Slab-on-Grade Homes
• Drainage Systems
• Under Slab Ductwork
• Radon Mitigation Systems and Moisture
• Air Filtration Systems

Some Key Elements To Radon Mitigation

A state or nationally qualified contractor should install a system in accordance with the standards or guidance of the state license/certification or national proficiency program that has certified them. There are three standards that may be in use by states or proficiency programs. They are to a great extent, consistent with each other. In addition, some states (FL, IL, PA) have their own standards. The standards are:

• US EPA, 1994, Radon Mitigation Standards
• ASTM Standard Practice for Installing Radon Mitigation Systems in Low-Rise Residential Buildings E2121
• AARST, 2006, ASD Radon Mitigation Standards (June 2006)

The standards provide helpful, specific guidance. For example:

• The discharge shall be at least 10 feet above grade, 10 feet away from any opening that is less than two feet below the discharge, and above or at the eave of the roof.
• The piping may also be routed up the outside the home, but the discharge must still meet the above criteria
• System fans should not be located inside the home or in a crawlspace. They can be in an attic, outdoors, or in a garage, provided there is no living space above the garage.
• There should be an indicator located in a prominent location that will easily indicate to the occupant that the system is functioning properly.
• Power to the fan should be run in accordance with local electric codes; including permits where required.
• All portions of the system are to be labeled and a simple instruction manual, with warranties, provided to the homeowner.
• All homes with mitigation systems should be retested no sooner than 24 hours (nor later than 30 days) after installation to verify reduction. The home should also be retested every two years.

Crawl Spaces

A high density polyethylene sheet is laid on the soil. The seams are sealed, and the edges are sealed to the foundation walls. A perforated pipe or drain mat may be placed beneath the plastic. This pipe is typically connected to solid PVC piping and fan, which creates a vacuum beneath the plastic. This effectively collects the radon and exhausts it to a safe location outside.

Slab on Grade Homes

At least one four to six inch hole is cored (drilled) through the slab. A small pit is hollowed out beneath the hole, and a PVC pipe is inserted. This pipe is routed to a fan that creates a vacuum beneath the slab. The number of suction points depends on the permeability of the soil beneath the slab and the number of footings within the building.

A single radon vent pipe is often all that is required in a residence. 

Drainage Systems

Homes that have sumps or French drains for control of rainwater may be effectively mitigated utilizing the sump to collect radon from the underlying soil, or a separate hole may be used.

Under Slab Ductwork

In some homes, return-air ductwork for the forced-air conditioning system is located beneath a slab floor. Although this can increase usable interior space and reduce the noise of recirculating air inside the home, the sub-floor ductwork, if unsealed, can add to radon problems. When the air conditioner fan is on, a fairly large vacuum effect created in the buried ductwork can draw radon-laden soil gas through the ducts and into the living space.

Even with this type of construction, there are effective ways to reduce radon. For example, if a house has a sump, a four-inch pipe connected to a sealed lid on the sump can route incoming soil gases to the radon fan. If the house has a perimeter foundation drain (French Drain), the vent pipe can be connected to the drain, taking care not to interfere with water drainage or sump pump function.

For those houses, radon drawn inside through sub-floor ducts may require extra attention.

Radon Mitigation Systems and Moisture

Soil air drawn from beneath a basement floor is commonly high in moisture vapor. If your radon mitigation system is not installed properly, this moisture vapor will condense and pool inside the ventilation pipe. Moisture vapor that pools in an unheated area may freeze at low temperatures. 

A properly designed and constructed radon mitigation system will prevent radon gas and may reduce soil moisture vapor from intruding into your home. A fringe benefit of a radon system may be a drier basement space.

Air Filtration Systems

Since it is the decay products of radon that actually present the risk from elevated radon levels, some homeowners have installed high efficiency air filters (HEPA) in their homes to not only reduce radon decay products, but also to reduce other airborne particulates that can complicate allergies. These systems will not affect radon levels.